1. Field of the Invention
The invention relates generally to non-invasive methods and systems for probing the earth, and more specifically to radars that can image and detect landmines and other similar anomalies in the ground. And in particular, such landmine detection systems in which the users are guided by navigation devices.
2. Description of the Prior Art
Many valuable and/or dangerous objects are buried in the ground, and digging them up to see what is there is often not possible or practical. A number of different physical phenomena have been used as the basis of various kinds of non-invasive probes, e.g., electromagnetic, radar, and neutron-gamma signature. Metal detectors are commonly used by treasure hunters to find coins and other metal objects buried in the ground. Ground-penetrating radars have been developed as another way to xe2x80x9cseexe2x80x9d what is underground without damaging or setting-off the buried objects. Such radars have been very useful in locating certain types of anti-personnel and anti-tank landmines.
Michael D. Bashforth, et al., describe a wide band stepped frequency ground penetrating radar in U.S. Pat. No. 5,499,029, issued Mar. 12, 1996. Such relates to attempts to increase the average signal power and to preserving phase information so digital signal processing can extract more information about objects in the soil. The radar transmitter steps in frequency from 100 MHz to 1,000 MHz, and data is taken at 2.0 MHz step intervals. Both in-phase and quadrature data are collected for over 900 samples. The received signals are combined with samples from the transmitter to detect any phase shifting that may have been caused by objects in the ground, e.g., landmines and waste containers.
The present inventors, Larry Stolarczyk and Gerald Stolarczyk, describe the measuring of the thickness of ground deposit layers with a microstrip antenna, in U.S. Pat. No. 5,072,172, issued Dec. 10, 1991. Interpolation tables are used to lookup the layer thickness values corresponding to antenna conductance and resonance measurements. Such resonant microstrip patch antenna (RMPA) and their resulting measurements are used to guide coal-seam drum-cutter equipment for more efficient mining of natural deposit ores. The RMPA driving-point impedance (S11) changes significantly when a solid, gas, or liquid layer thickness overlying the RMPA varies.
The RMPA can be swept above a soil surface to find buried landmines, utilities, and other shallow-buried objects. These objects don""t necessarily need to be made of metal to be found. What is needed is that the dielectric constants of the objects and the medias they are buried in must differ, e.g., for contrast.
U.S. Pat. No. 5,769,503, issued Jun. 23, 1998 to Stolarczyk, et al., describes mounting such RMPA on a rotating drum or arm of a coal, trona, or potash mining machine. A ground-penetrating-radar transmitting antenna and a receiving antenna can be mounted on a cutting drum to detect deeply buried objects and anomalous geology just ahead of the mining. A radar frequency downconverter is used so low-cost yet-accurate measurement electronics can be built. A first phase-locked loop (PLL) is operated at the resonant frequency of the patch antenna or at each sequentially stepped radar frequency. A second PLL is offset from the first PLL by an intermediate frequency (IF) and is called a tracking PLL. The measurement speed can be delayed by the sequential way in which the PLL""s lock on to signals, so a solution to that delay is described.
Many unfortunate tragedies have resulted from mine fields that were supposedly xe2x80x9cclearxe2x80x9d. The fault is not in the detectors themselves, but in the way they are used. A typical handheld-portable detector mounted on a mast is swung left and right while the user moves forward. This results in a Z-pattern with open folds at each extreme. If the forward progress is too fast, some parts of the lane may not be thoroughly probed. If these skipped parts conceal consequentially undetected landmines, a tragedy thereafter lies in wait.
Briefly, a landmine detection system embodiment of the present invention comprises a ground-penetrating radar for probing the surface of the ground for landmines and other anomalies. The radar is swept back and forth across a lane while a user proceeds forward. A navigation sensor and processor keep track of all the parts of the lane that have been probed. A user display presents a visual graphic that represents the lane and the parts of it that have been probed. The user is then able to swing the radar to areas that are indicated as having been skipped in previous passes, e.g., to get 100% coverage.
An advantage of the present invention is that a ground-penetrating radar is provided that finds landmines and other objects buried in the ground.
A further advantage of the present invention is that a landmine detection system is provided that assists the user in obtaining 100% coverage of lanes through mine fields.
A still further advantage of the present invention is that a landmine detection system is provided that can coordinate and share its findings with its peers.
Another advantage of the present invention is a landmine detection system is provided that can indicate where to begin sweeping according to downloaded coordinates.
These and other objects and advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiment which is illustrated in the various drawing figures.